Field
Embodiments described below relate to a semiconductor device.
Description of the Related Art
One kind of semiconductor memory device is a flash memory. In particular, a NAND type flash memory is generally widely used since it is low cost and has a large capacity. Moreover, up to now, many technologies for further increasing the capacity of this NAND type flash memory have been proposed. One such technology is a structure in which memory cells are disposed three-dimensionally. In such a three-dimensional type semiconductor memory device, the memory cells are disposed in a certain direction, and, from each of those memory cells disposed in the certain direction, conductive layers extend in a horizontal direction to a substrate and are stacked in a vertical direction to the substrate.
In such a three-dimensional type semiconductor memory device, when the memory and the stacked number of conductive layers increases, the number of switching transistors for connecting the memory cells and an external circuit increases and an occupied area of the switching transistors increases. Therefore, it is required that the occupied area of these switching transistors is reduced.